| | | Hi! | | | I'm a process engineer attempting to do a capability study on our existing convection reflow oven - Heller 1500. It was recommended by an independent consultant to do at the very least, load testing, process ready testing, and board uniformity heating testing. However, I'm confused about how to establish spec. limits and how to calculate meaningful Cp and Cpk values for the characteristics that drive defects. I really don't have the liberty at this time to do a design of experiment. I co-worker of mine says that I should be keying in on the ability of the oven to achieve and maintain the solder paste manufacturer's recommended reflow profile and not the characteristics mentioned above. Any suggestions? Will you elaborate on what I'm trying to do? Quite frankly, I'm not sure myself! Will you share any documentation on this subject? Perhaps you did something similar. Thank you in advance for your time and consideration. Best regards! | | | | | John: So, why did you let that consultant out of the room without explaining to you what he/she was talking about? ;-) | | | | In part, your co-worker is correct. One of the prerequisites of doing any Cp / Cpk stuff is that the process in control. And you don�t know if your in control. So, why not do this? | | | | 1 Collect some data on time over liquidous, and maybe ramp rate. | | 2 Chart the data. | | 3 Convince yourself you have a solid process. | | 4 Calculate the Cp / Cpk stuff. | | 5 Consider load testing, process ready testing, and board uniformity heating testing. | | | | Call Marc Peo or Dave Jenkins in Sales at Heller 201.377.6800 and explain your dilemma. They�ve seen enough wacky testing requirements to gag a moose. | | | | Ta | | | | Dave F | | | John, | | Dave brings up some great points. I would also like to add that the most common parameters used to evaluate Cp and Cpk are peak temperature and liquidous time. | | Additionally, to achieve more meaningful Cp and Cpk information it is important to assign appropriate tolerances to each of the parameters. Typically we have seen a range of +/- 3 to 5 degrees c as the tolerance for peak temperature and +/- 5 to 10 seconds for liquid time. | | However, I suggest you look to the paste mfr for guidance on these tolerances. Different pastes have different requirements and the paste mfr. has the best knowledge of what is important and what is not. | | Hope this helps. Feel fre to call with any questions. | | Best Regards, | | Marc | So, did the "consultant" mention other brands in the same breath?:[
I've heard of tests such as 'turbulance' and it's effect on 0402's (???) but what does that mean when they're stuck in paste? Or what a board experiences between two huge blocks of aluminum, when was the last time you put aluminum in your oven? All the oven vendors that are recognized in the industry have already been able to meet these issues and they can all melt solder paste very well!
I have a 1500 that I'm very happy with. The bottom line is solder joint quality and that comes with the correct profile (do you have a solid process?). When in doubt, profile. I've been able to "eliminate" shorts by paying attention to profile and ramp rates. Also, have the oven calibrated. Uniformity is important, I've adjusted my rails accordingly.
Once you've done this then the Cp & Cpk can help you tweek the process once you've fixed the printing problem(s) with the paste, the paste's affect over time, tack time, etc.. Remember, 80% of your problems will be in the printing process/solder paste, the other major effort is in your oven profile. My solder paste specialist (Arlene) has tons of stories where wrong profiles are used, often unintentionally or they just didn't read the specs! Make your solder paste specialist a member of your team and lots of these issues will fall in place.
Don't let the trees get in your way of seeing the forest, solve your real problems first. Let Perato rule here.
Good Luck, Scott
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Hi!
I'm a process engineer attempting to do a capability ...
- Jul 07, 1999
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